The present invention generally relates to the field of two-dimensional video displays, and more specifically, to a video display with integrated control circuitry formed on a dielectrically insulating substrate such as sapphire.
The display market is dominated by cathode ray tube (CRT) technology. While offering multi-color high resolution images, CRT displays have performance limitations related to difficulty in scaling to large size, inability to operate at low voltages and low power consumption, and constructing ruggedized displays. To circumvent these limitations, flat panel display technologies including liquid crystal, plasma discharge (PD), field emission (FED), electroluminescent (EL) type displays, micromachined digital displays and the like have been investigated.
Liquid crystal displays are used in a wide variety of commercial applications, including portable computers, wristwatches, camcorders, and large screen televisions. Liquid crystal displays are fabricated on transparent glass or quartz substrates do not generally support the manufacture of high quality electronic materials. This is due to the inherent inability to deposit defect-free, single crystal semiconductor layers on glass or quartz arising from the respective lattice incoherence or mismatch, and the difference in the coefficients of thermal expansion. PD and EL displays are beginning to find their way into the marketplace, primarily in portable computers. However, these types of displays also are fabricated on substrates that do not support the manufacture of high quality electronic devices. The operation of all these type of displays are controlled by integrated circuits. However, the integration of such display driving circuitry with the displays has been limited to thin film transistor technology using amorphous (.alpha.-Si) or polycrystalline (poly-Si) silicon deposited on the glass or quartz substrate. The intrinsic properties of amorphous and polycrystalline silicon, such as lattice and thermal mismatch between the circuit layers, and the low temperature deposition techniques used to fabricate such circuits result in a silicon layer with poor charge carrier mobility and crystallographic defects which cause electronic performance limitations such as frequency response and refresh rate.
Of particular importance for integrated displays is the desire for higher density circuitry for ultra-high resolution display applications. Existing material quality is insufficient due to leakage paths which occur in small scale, high density circuitry fabricated in .alpha.-Si and poly-Si. Furthermore, compatibility with very large scale integration would allow integration of video drivers, digital logic and other computational circuitry on-chip thereby offering greater functionality, higher reliability, and improved performance.